1. Field of the Invention
The present invention relates to a method for manufacturing a magnetic sensor using a magnetoresistance element (so-called synthetic spin valve film) having a multifilm laminated fixed layer, to a magnet array suited for use in the method, and to a method for manufacturing the magnet array.
2. Description of the Related Art
A conventionally known giant magnetoresistance element (hereinafter referred to as a “GMR element”) includes a fixed layer that includes a pinned layer, and a pinning layer for pinning the magnetization of the pinned layer in a fixed direction; a free layer whose magnetization direction varies in accordance with an external magnetic field; and a spacer layer disposed between the pinned layer and the free layer and made of a nonmagnetic electric conductor. The resistance of the GMR element varies in accordance with the angle between the magnetization direction of the pinned layer and the magnetization direction of the free layer. In other words, the resistance of the GMR element varies in accordance with a component of the external magnetic field aligned with the magnetization direction of the pinned layer. Therefore, the magnetic detection direction of the GMR element coincides with the magnetization direction of the pinned layer.
The GMR element is used in magnetic sensors, such as a terrestrial magnetism sensor. In such an application, even when the GMR element is exposed to a strong magnetic field or high temperature, its fixed layer must exhibit stable magnetization. If the magnetization of the fixed layer varies, the resistance characteristic of the GMR element will vary. In order to meet the requirement, there has been developed a GMR element (so-called synthetic spin valve film) in which the conventional fixed layer is replaced with a multifilm laminated fixed layer.
A pinned layer of the multifilm laminated fixed layer includes a first ferromagnetic film adjacent to a spacer layer; a second ferromagnetic film laminated on the first ferromagnetic film; and an exchange-coupling film sandwiched between the first ferromagnetic film and the second ferromagnetic film. A pinning layer of the multifilm laminated fixed layer is made of antiferromagnet and is laminated on the second ferromagnetic layer. The pinning layer is exchange-coupled to the second ferromagnetic layer to thereby pin the magnetization of the second ferromagnetic film in a fixed direction. The first ferromagnetic film and the second ferromagnetic film are exchange-coupled to each other via the exchange-coupling film, whereby the magnetization of the first ferromagnetic film is pinned in a fixed direction (e.g., refer to Japanese Patent No. 2786601 (paragraphs 0016 to 0024 and FIG. 5)).
Meanwhile, a magnetic sensor (e.g., terrestrial magnetism sensor) that utilizes a GMR element and is adapted to detect the direction of an external magnetic field requires at least two GMR elements of different magnetic detection directions. The direction of the external magnetic field coincides with the direction of a resultant vector of two vectors of the magnetic field, which two vectors are detected by the two GMR elements, respectively, and aligned with the magnetic detection directions of the two GMR elements, respectively. Such a magnetic sensor is called a biaxial magnetic sensor.
In order to pin the magnetization of a pinned layer of a synthetic spin valve film, a step in which an element film is held at high temperature for a predetermined period of time while a very strong magnetic field is applied thereto (heat treatment process) must be performed. Accordingly, in order to reduce the size of a biaxial magnetic sensor, which uses two GMR elements whose synthetic spin valve films are of different magnetic detection directions, two strong magnetic fields whose directions differ from each other (e.g., the directions are perpendicular to each other) must be generated at close positions. However, generation of such magnetic fields is very difficult. As a result, a small-sized biaxial magnetic sensor using a synthetic spin valve film has encountered difficulty in mass production.